1. Field of the Invention
The present invention relates to a pattern defect detecting system and more particularly to a pattern defect detecting system which detects defects or foreign matters on the surface of a regularly arranged test pattern such as an integrated semiconductor circuit which has been subjected to patterning, using an optical space modulator capable of recording and erasing diffracted light of a test sample in real-time operations as spatially filtering means.
2. Prior Art
Heretofore, as a pattern defect detecting system of this type there has been known, for example, the one disclosed in Japanese Patent Publication No. 16542/81, in which there is made inspection of pattern using a transmitted image of a test sample.
On the other hand, as a like system using a reflected image of a test sample there has been proposed by the same applicant the system described in the specification of Japanese Patent application No. 38770/87.
FIG. 1 is a block diagram illustrating such a conventional reflection type pattern defect detecting system as referred to above. In FIG. 1, the reference numeral 1 denotes a coherent light source such as a laser; the numeral 2 denotes a collimator for enlarging the light emitted from the light source 1 into collimated light; numerals 5 and 32 each denote a half mirror; and numeral 4 denotes a test sample placed on a stage, the test article having a regularly arranged test pattern. Further, numeral 6 denotes an X-Y stage for moving the test sample 4 and numeral 7 denotes a convex lens for condensing the light reflected from the test sample 4. Numeral 12 denotes a defect detecting camera disposed in the position where the test sample 4 is imaged by the lens 7; numeral 13 denotes a signal processing section for processing an output signal provided from the camera 12, to detect a defective position; and numeral 14 denotes a monitor television connected to the signal processing section 13 to display the defect. Further, numeral 17 denotes a spatial filter disposed in a backfocal position of the lens 7 to cut off diffracted light based on a normal pattern of the test sample 4. Numeral 33 denotes a camera for detecting the position of a diffraction pattern based on reflected light in the post-focal position of the lens 7, and numeral 34 denotes a control unit which calculates the amount of dislocation from a normal position of the diffraction pattern and provides a correction command to tilt angle adjusting mechanisms 35, 36 and a rotational angle adjusting mechanism 37.
The operation of the above conventional system will now be described.
The light emitted from the coherent light source 1 is reflected by the half mirror 5 and then directed to the test pattern of the test sample 4. The reflected light from the test sample 4 passes through the half mirror 5 and condensed by the lens 7, then split into two light beams. One beam reaches the spatial filter 17, while the other is incident on the diffraction pattern position detecting camera 33. The spatial filter 17 exposes in that position the diffraction pattern of the normal pattern onto a photographic plate and after development processing it is returned exactly to the exposure position and fixed there. Next, during detection of a pattern defect, the diffracted light of the reflected light is observed by the camera 33 to detect the position of the diffraction pattern. The control unit 34 provides a command for correcting the deviation in tilt angle and that in rotational angle of the test sample 4 from the optical axis, to the adjusting mechanisms 35, 36 and the rotary stage 37. Then, registration is made between the diffraction pattern of the filter 17 and the diffracted light of the normal pattern of the test sample 4. As a result, the diffracted light of the normal pattern during the detection is removed by the diffraction pattern on the filter, a defect signal is observed by the camera 12, and the pattern defect is displayed on the monitor 14.
Thus, in the conventional pattern defect detecting system, when the tilt angle and rotational angle of the test sample vary with respect to the optical axis, there occurs deviation between the position of the diffraction pattern which appears on the post-focal plane of the lens and that of the diffraction pattern recorded on the filter. Consequently, every time the test sample is moved, there are detected deviations of tilt angle and rotational angle, so it is necessary to correct the above positions. This is inconvenient. Further, since the filter material is the photographic plate, a new filter must be prepared at every change in pattern of the test sample, thus requiring development processing in an off-line.